Cellular response to renal hypoxia is different in adolescent and infant rats

Acute kidney injury decreases pulmonary vascular growth and alveolarization in neonatal rat pups

BACKGROUND

Acute kidney injury (AKI) is common in sick neonates and associated with poor pulmonary outcomes, however, the mechanisms responsible remain unknown. We present two novel neonatal rodent models of AKI to investigate the pulmonary effects of AKI.

METHODS

In rat pups, AKI was induced surgically via bilateral ischemia-reperfusion injury (bIRI) or pharmacologically using aristolochic acid (AA). AKI was confirmed with plasma blood urea nitrogen and creatinine measurements and kidney injury molecule-1 staining on renal immunohistochemistry. Lung morphometrics were quantified with radial alveolar count and mean linear intercept, and angiogenesis investigated by pulmonary vessel density (PVD) and vascular endothelial growth factor (VEGF) protein expression. For the surgical model, bIRI, sham, and non-surgical pups were compared. For the pharmacologic model, AA pups were compared to vehicle controls.

RESULTS

AKI occurred in bIRI and AA pups, and they demonstrated decreased alveolarization, PVD, and VEGF protein expression compared controls. Sham pups did not experience AKI, however, demonstrated decreased alveolarization, PVD, and VEGF protein expression compared to controls.

CONCLUSION

Pharmacologic AKI and surgery in neonatal rat pups, with or without AKI, decreased alveolarization and angiogenesis, producing a bronchopulmonary dysplasia phenotype. These models provide a framework for elucidating the relationship between AKI and adverse pulmonary outcomes.

IMPACT

There are no published neonatal rodent models investigating the pulmonary effects after neonatal acute kidney injury, despite known clinical associations. We present two novel neonatal rodent models of acute kidney injury to study the impact of acute kidney injury on the developing lung. We demonstrate the pulmonary effects of both ischemia-reperfusion injury and nephrotoxin-induced AKI on the developing lung, with decreased alveolarization and angiogenesis, mimicking the lung phenotype of bronchopulmonary dysplasia. Neonatal rodent models of acute kidney injury provide opportunities to study mechanisms of kidney-lung crosstalk and novel therapeutics in the context of acute kidney injury in a premature infant.

Hypoxia-Induced Kidney Injury in Newborn Rats

Exposure to hypoxia during the early postnatal period can have adverse effects on vital organs. Neonatal Sprague-Dawley rats housed in a hypoxic chamber were compared to those in a normoxic chamber from postnatal days 0 to 7. Arterial blood was collected to evaluate renal function and hypoxia. Kidney morphology and fibrosis were evaluated using staining methods and immunoblotting. In the kidneys of the hypoxic group, protein expressions of hypoxia-inducible factor-1 were higher than those in the normoxic group. Hypoxic rats had higher levels of hematocrit, serum creatinine, and lactate than normoxic rats. Body weight was reduced, and protein loss of kidney tissue was observed in hypoxic rats compared to normoxic rats. Histologically, hypoxic rats showed glomerular atrophy and tubular injury. Renal fibrosis with collagen fiber deposition was observed in the hypoxic group. The expression of nicotinamide adenine dinucleotide phosphate oxidases was enhanced in the kidneys of hypoxic rats. Proteins involved in apoptosis were upregulated in the kidneys of hypoxic rats. An increase in the expression of pro-inflammatory cytokines was also observed in the kidneys of hypoxic rats. Hypoxic kidney injury in neonatal rats was associated with oxidative stress, inflammation, apoptosis, and fibrosis.

Intermittent hypoxia retards mandibular growth and alters RANKL expression in adolescent and juvenile rats

OBJECTIVES

Chronic intermittent hypoxia (IH), a common state experienced in obstructive sleep apnoea (OSA), retards mandibular growth in adolescent rats. The aim of this study was to elucidate the differential effects of IH on mandibular growth in different growth stages.

MATERIALS AND METHODS

Three-week-old (juvenile stage) and 7-week-old (adolescent stage) male Sprague-Dawley rats underwent IH for 3 weeks. Age-matched control rats were exposed to room air. Mandibular growth was evaluated by radiograph analysis, micro-computed tomography, real-time polymerase chain reaction and immunohistology. Tibial growth was evaluated as an index of systemic skeletal growth.

RESULTS

IH had no significant impact on the general growth of either the juvenile or adolescent rats. However, it significantly decreased the total mandibular length and the posterior corpus length of the mandible in the adolescent rats and the anterior corpus length in the juvenile rats. IH also increased bone mineral density (BMD) of the condylar head in adolescent rats but did not affect the BMD of the tibia. Immunohistological analysis showed that the expression level of receptor activation of nuclear factor-κB ligand significantly decreased (in contrast to its messenger ribonucleicacid level) in the condylar head of adolescent rats with IH, while the number of osteoprotegerin-positive cells was comparable in the mandibles of adolescent IH rats and control rats.

LIMITATIONS

The animal model could not simulate the pathological conditions of OSA completely and there were differences in bone growth between humans and rodents.

CONCLUSIONS

These results suggest that the susceptibility of mandibular growth retardation to IH depends on the growth stage of the rats.

Fluid management, electrolytes imbalance and renal management in neonates with neonatal encephalopathy treated with hypothermia

Kidney dysfunction and acute kidney injury (AKI) frequently accompanies neonatal encephalopathy and contributes to neonatal morbidity and mortality. While there are currently no proven therapies for the treatment of AKI, understanding the pathophysiology along with early recognition and treatment of alterations in fluid, electrolyte and metabolic homeostasis that accompany AKI offer opportunity to reduce associated morbidity. Promising new tests and technologies, including urine and serum biomarkers and renal near-infrared spectroscopy offer opportunities to improve diagnosis and monitoring of neonates at risk for kidney injury. Furthermore, recent advances in neonatal kidney supportive therapies such as hemofiltration and hemodialysis may further improve outcomes in this population. This chapter provides an overview of disorders of fluid balance, electrolyte homeostasis and kidney function associated with neonatal encephalopathy and therapeutic hypothermia. Recommendations for fluid and electrolyte management based upon published literature and authors' opinions are provided.

Comparative Study of the Severity of Renal Damage in Newborn and Adult Rats under Conditions of Ischemia/Reperfusion and Endotoxin Administration

Oxidative kidney injury was compared in newborn and adult rats under conditions of ischemia/reperfusion and in experimental model of systemic inflammation induced by endotoxin (LPS of bacterial cell wall) administration. Oxidative stress in the kidney accompanied both experimental models, but despite similar oxidative tissue damage, kidney dysfunction in neonates was less pronounced than in adult animals. It was found that neonatal kidney has a more potent regenerative potential with higher level of cell proliferation than adult kidney, where the level proliferating cell antigen (PCNA) increased only on day 2 after ischemia/reperfusion. The pathological process in the neonatal kidney developed against the background of active cell proliferation, and, as a result, proliferating cells could almost immediately replace the damaged structures. In the adult kidney, regeneration of the renal tissue was activated only after significant loss of functional nephrons and impairment of renal function.

Transcriptional regulators of Na,K-ATPase subunits

The Na,K-ATPase classically serves as an ion pump creating an electrochemical gradient across the plasma membrane that is essential for transepithelial transport, nutrient uptake and membrane potential. In addition, Na,K-ATPase also functions as a receptor, a signal transducer and a cell adhesion molecule. With such diverse roles, it is understandable that the Na,K-ATPase subunits, the catalytic α-subunit, the β-subunit and the FXYD proteins, are controlled extensively during development and to accommodate physiological needs. The spatial and temporal expression of Na,K-ATPase is partially regulated at the transcriptional level. Numerous transcription factors, hormones, growth factors, lipids, and extracellular stimuli modulate the transcription of the Na,K-ATPase subunits. Moreover, epigenetic mechanisms also contribute to the regulation of Na,K-ATPase expression. With the ever growing knowledge about diseases associated with the malfunction of Na,K-ATPase, this review aims at summarizing the best-characterized transcription regulators that modulate Na,K-ATPase subunit levels. As abnormal expression of Na,K-ATPase subunits has been observed in many carcinoma, we will also discuss transcription factors that are associated with epithelial-mesenchymal transition, a crucial step in the progression of many tumors to malignant disease.

Cellular biology of end organ injury and strategies for prevention of injury

The interruption of placental blood flow induces circulatory responses to maintain cerebral, cardiac, and adrenal blood flow with reduced renal, hepatic, intestinal, and skin blood flow. If placental compromise is prolonged and/or severe, total circulatory failure is likely with cerebral hypoperfusion and resultant hypoxic ischemic cerebral injury with collateral renal, cardiac, and hepatic injury. Management strategies should be targeted at restoring cerebral perfusion and oxygen delivery and minimizing the extent of secondary injury. Specifically, the focus should include the judicious use of supplemental oxygen, avoidance of hypoglycemia and elevated temperature in the delivery room, and the early administration of therapeutic hypothermia to high-risk infants.

Modulation of renal cell injury by heat shock proteins: lessons learned from the immature kidney

The mechanisms that underlie tolerance to injury in immature animals and tissues have been a subject of interest since 1670. Observations in neonatal units that premature infants are less prone to develop acute renal failure than adults in critical care units have prompted a series of investigations. Although initially attributed to metabolic adaptation such as increased glycolytic capacity and preservation of high energy phosphate, more recent studies have indicated a prominent role for the heat shock response. Observed modulations of injury by heat shock proteins in the immature kidney have significant implications for advancement of our understanding of renal cell injury in both adults and children.

Exogenous human recombinant interleukin-10 protects the kidney against hypoxia-induced renal injury in immature rats

AIM

The purpose of this study was to determine the effects of exogenous human recombinant interleukin-10 (rhIL-10) on hypoxia-induced renal injury in immature rats.

METHOD

The study was performed on 1-day-old Sprague-Dawley rat pups. Group 1 (n = 8) served as non-hypoxic controls. Group 2 (untreated, n = 8) rats were subjected to hypoxia-reoxygenation (H/O) and were then returned to their mothers. Group 3 (rhIL-10 treated, n = 8) rats were subjected to H/O, were returned to their mothers, and were treated with rhIL-10 (75 microg/kg subcutaneously) for the next 3 days. All animals were killed on day 4 and renal specimens were obtained to determine the tissue level of malondialdehyde (MDA) and histological changes.

RESULTS

In the untreated group, moderate or severe renal tubular necrosis was observed However, the tubular necrosis score was significantly less in the rhIL-10 treated rats than in the untreated rats (P < 0.05). In the untreated group, MDA levels were significantly increased compared with the control and rhIL-10 groups (P < 0.001 and P < 0.05, respectively). In the rhIL-10 treated group, MDA levels were not significantly different compared with the control group.

CONCLUSION

RhIL-10 has a protective effect against hypoxia-induced renal injury in immature rats by depression of tissue MDA level and renal tubular necrosis score.

Room-air resuscitation causes less damage to heart and kidney than 100% oxygen

RATIONALE

Pure oxygen causes more oxidative stress than room air in resuscitation of asphyctic neonates, and consequently could be associated with increased tissue damage.

OBJECTIVES

To compare damage caused to heart and kidneys on reoxygenation in severely asphyctic term neonates resuscitated with room air (RAR) or 100% oxygen (OxR). Nonasphyctic term newborn infants served as a control group.

METHODS AND MEASUREMENTS

This is a prospective randomized clinical trial masked for the gas mixture. Reduced glutathione (GSH), oxidized glutathione (GSSG), and superoxide dismutase (SOD) activity were measured to assess oxidative stress. Plasma cardiac troponin T (cTnT) and urinary N-acetyl-glucosaminidase (NAG) assessed cardiac and renal damage, respectively. Daily determinations of NAG for a 2-wk period were performed to monitor postasphyctic renal damage.

MAIN RESULTS

Both asphyctic groups showed oxidative stress when compared with the control group as evidenced by diminished GSH/GSSG ratios, adaptive increases in SOD activity, and higher values of NAG and cTnT (markers of tissue damage). However, the OxR group showed significantly higher values of NAG and cTnT, lower GSH/GSSG ratios, and higher SOD activity than the RAR group. Moreover, NAG values persisted in being higher than normal in the OxR group for 2 wk after birth, whereas NAG in the RAR group dropped to normal within the first week. A linear correlation between cTnT or NAG and GSSG was found.

CONCLUSIONS

The use of room air on resuscitation causes less oxidative stress and damage to heart and kidney than pure oxygen.

Impaired kidney growth in low-birth-weight children: Distinct effects of maturity and weight for gestational age

BACKGROUND

Chronic kidney disease (CKD) alters the regulation of calcium and phosphate homeostasis, leading to secondary hyperparathyroidism, metabolic bone disease, soft tissue calcifications, and other metabolic derangements that have a significant impact on morbidity and mortality. The parathyroid gland is the central organ responsible for regulating these adaptive responses. Suppression of parathyroid hormone (PTH) secretion, hypertrophy, and hyperplasia are a major goal of treatment of CKD.

METHODS

Current literature was reviewed and combined with the author's experience to address a number of issues regarding the optimal treatment of secondary hyperparathyroidism in hemodialysis patients.

RESULTS

The calcium sensing receptor (CASR) is the most important factor regulating parathyroid gland function, and allosteric modulators of CASR, called calcimimetics, provide a novel drug therapy to suppress PTH secretion. The current use of active vitamin D analogues to suppress PTH is often limited by hypercalcemia and hyperphosphatemia. Clinical trials of cinacalcet HCl, the first calcimimetic to be approved for treatment of secondary hyperparathyroidism in CKD, have demonstrated suppression of circulating PTH levels without increments in the calcium-phosphorus (Ca x P) product, making it easier to achieve the stringent management guidelines proposed for subjects with CKD by the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI).

CONCLUSION

The management of disordered calcium and phosphate homeostasis in CKD patients is evolving based on our knowledge of the major importance of the calcium sensing receptor (CASR) in controlling parathyroid gland function and the potent actions of calcimimetics to target CASR. The purpose of this presentation is to provide an overview of the role of the CASR in regulation of parathyroid gland function, to examine the mechanisms whereby calcimimetics target the CASR, and to review the clinical trials that support the use of cinacalcet HCl for the treatment of secondary hyperparathyroidism in stage 5 chronic kidney disease (CKD).

Growth patterns of the heart and kidney suggest inter-organ collaboration in facultative fetal growth

Maternal smoking during pregnancy has been associated with a number of negative sequelae among offspring, including elevated postnatal blood pressure. While animal studies have described organ level alterations with smoke exposure, human data have been more limited. Thirty-four healthy maternal/fetal pairs (24 nonsmokers, 10 smokers) participated in a longitudinal growth study from the thirteenth week of pregnancy to document fetal kidney and heart growth trajectories and morphology. Curve fitting followed by a mixed model for repeated measures identified significantly different growth patterns in kidney width, thickness, length, and volume growth with exposure: the smoke-exposed fetal kidney was wide and thick compared to the unexposed kidney during the second and early third trimester, declining to proportionately thin kidneys for length and width subsequently. Cardiac growth in width and volume followed a reverse pattern: a surge in cardiac volume occurred after 30 weeks with acceleration in cardiac width, resulting in a heart that was wide for length and for fetal weight. Smoke exposure altered fetal growth in size and timing of the heart and kidneys during midgestation, with changes in organ morphology suggesting compensatory growth. These are the first data providing anatomical evidence of altered renal/cardiac volume relationships that may provide a mechanism to previously reported sequelae of in utero smoke exposure. They suggest that cell-level adaptive responses to hypoxia and/or chemical insults are operative and illustrate the importance of longitudinal ultrasound to directly assess the organ-level growth response of the human fetus to a prenatal stress, in lieu of relying on birth outcome measures.